Robert Shelby, a former Army combat engineer, knocked over the first domino.

As a U.S. district judge — appointed in 2012 by President Barack Obama with support from Utah's two conservative Republican senators — Shelby ruled last December that the state's voter-approved ban on same-sex marriage was unconstitutional.

Since then, in an unbroken string of victories for gay-marriage backers, a dozen other judges in states across the nation have followed suit by overturning bans or ordering states to recognize gay marriages from out of state.

Collectively, these judges are diverse — white and black, male and female, gay and straight, some appointed by Democratic presidents and some by Republicans. However, they seemed to draw common inspiration from a U.S. Supreme Court ruling in June 2013 that ordered the federal government to recognize same-sex marriages.

In most of the cases, the rulings have been stayed pending appeals, and a final nationwide verdict on same-sex marriage will likely come from the Supreme Court as some of the cases head there. But the judges' opinions — often embellished by soaring language — reflected a yearning to be on what they had come to see as the right side of history.

Shelby, in his 53-page decision, said the constitutional amendment that Utah voters approved in 2004 violated gay couples' rights to due process and equal protection. The state, he said, failed to show that allowing same-sex marriages would affect opposite-sex marriages in any way.

"In the absence of such evidence, the State's unsupported fears and speculations are insufficient to justify the State's refusal to dignify the family relationships of its gay and lesbian citizens," Shelby wrote.

A look at some of other judges and their rulings:

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MICHIGAN:

Long before the current spate of marriage litigation, Detroit-based U.S. District Judge Bernard Friedman learned firsthand about the aspirations of gays and lesbians seeking to raise families.

Friedman, a Republican appointed to the federal bench in 1988 by President Ronald Reagan, hired an openly gay University of Michigan Law School student as his clerk in 1995. The clerk, Judith Levy, went on to bear children and this year became a federal judge in Michigan.

In March, Friedman — now 70 — struck down the gay-marriage ban approved by Michigan voters in 2004. The day after his ruling, in a brief window before a stay was issued, Levy performed several same-sex marriages.

The case was initiated by two Detroit-area nurses seeking to overturn Michigan's law banning joint adoptions by gay couples. They later expanded it to challenge the marriage ban itself.

"State defendants lost sight of what this case is truly about: people," Friedman wrote in his opinion. "No court record of this proceeding could ever fully convey the personal sacrifice of these two plaintiffs who seek to ensure that the state may no longer impair the rights of their children and the thousands of others now being raised by same-sex couples."

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VIRGINIA

With experience as a no-nonsense federal prosecutor and also as a public defender, Arenda L. Wright Allen saw the justice system from both sides. She won unanimous Senate confirmation in 2011 when Obama appointed her as the first black woman to serve on the federal bench in Virginia.

In February, after a high-profile trial, she overturned Virginia's voter-approved ban on same-sex marriage with an opinion that evoked civil rights struggles of America's past.

"Justice has often been forged from fires of indignities and prejudices suffered," she wrote. "We have arrived upon another moment in history when We the People becomes more inclusive, and our freedom more perfect."

She also noted that Virginia was the focal state when the U.S. Supreme Court struck down state laws against interracial marriage in 1967.

"Tradition is revered in the Commonwealth, and often rightly so," Wright Allen wrote. "However, tradition alone cannot justify denying same-sex couples the right to marry any more than it could justify Virginia's ban on interracial marriage."

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ARKANSAS

Four years ago, a judge little known outside of Arkansas made waves by overturning a state law that prevented gays and lesbians from adopting or fostering children. It was a harbinger of things to come. On May 9, that same jurist, Pulaski County Circuit Court Judge Chris Piazza, struck down Arkansas' ban on gay marriages.

The first same-sex marriages in the South ensued, before a stay was issued. Former Gov. Mike Huckabee, among others, was not pleased.

"Allowing one single member of the judicial branch to become Lord God of law is dangerous and unconstitutional," Huckabee wrote.

However, any voters upset by Piazza's ruling can't vent their frustration at the polls — the 67-year-old judge didn't draw a challenger in his bid for re-election this year and will serve another six years.

"It has been over 40 years since Mildred Loving was given the right to marry the person of her choice," Piazza wrote. "The hatred and fears have long since vanished and she and her husband lived full lives together; so it will be for the same-sex couples. It is time to let that beacon of freedom shine brighter on all our brothers and sisters. We will be stronger for it."

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OREGON

Michael McShane, one of a small number of openly gay federal judges, harkened back to his own youth in his ruling May 19 striking down Oregon's voter-approved 2004 ban on gay marriage.

"Generations of Americans, my own included, were raised in a world in which homosexuality was believed to be a moral perversion, a mental disorder, or a mortal sin," he wrote. "I remember that one of the more popular playground games of my childhood was called 'smear the queer.'"

In preliminary court proceedings, the question was raised as to whether McShane — as a gay man raising a child with his partner — should recuse himself. However, McShane said he had never attended a rally or spoken publicly about gay marriage, and the issue was not vigorously pursued by gay-marriage opponents.

In his ruling, McShane extolled the same-sex couples who had filed the lawsuit.

"I believe that if we can look for a moment past gender and sexuality, we can see in these plaintiffs nothing more or less than our own families," he wrote. "With discernment we see not shadows lurking in closets or the stereotypes of what was once believed; rather, we see families committed to the common purpose of love, devotion, and service to the greater community."

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PENNSYLVANIA

Before last week, U.S. District Judge John E. Jones III was perhaps best known for handling of one of the biggest courtroom clashes between faith and evolution since the 1925 Scopes Monkey Trial. In a 2005 decision, Jones barred the Dover Area School District in southern Pennsylvania from teaching "intelligent design" in biology class, saying its first-in-the-nation curriculum decision violated the constitutional separation of church and state.

On May 20, Jones once again had an impact of the nation's culture wars, striking down a 1996 Pennsylvania law that was the Northeast's last ban on gay marriage.

A former small-town public defender and head of the state's Liquor Control Board, Jones was appointed to the federal bench in 2002 with the approval of Pennsylvania's two Republican U.S. senators, Arlen Specter and Rick Santorum. Santorum, an outspoken critic of same-sex marriage, called Jones "an outstanding litigator" during a confirmation hearing.

In his ruling on marriage, Jones said the plaintiffs — a widow, 11 couples and one of the couples' two teenage daughters — were courageous.

"We are a better people than what these laws represent, and it is time to discard them into the ash heap of history," Jones wrote.